Fix resolving device mapper related devices for non symlinks

Under certain circumstances files under `/dev/mapper` are not symlinks,
but instead device nodes. This was causing issues, as the code was
always expecting to find symlinks. A fix has been put into place, to
resolve the given device node to a path to a device mapper device under
`/dev`.

Author: patrickpichler

cmd/agent/daemon/pipeline/storage_info_provider.go

@@ -520,17 +520,37 @@ func (s *SysfsStorageInfoProvider) getBackingDevices(device string) []string {
 
 // getLVMDMDevice resolves LVM logical volumes to their dm device.
 // It handles the symlink chain: /dev/mapper/vg-lv → /dev/dm-X
+// It also handled block devices.
 func (s *SysfsStorageInfoProvider) getLVMDMDevice(device string) []string {
 	if !strings.HasPrefix(device, "/dev/mapper/") {
 		return nil
 	}
 	hostMapperPath := filepath.Join(s.hostRootPath, device)
-	linkTarget, err := os.Readlink(hostMapperPath)
-	if err != nil {
-		s.log.Errorf("symlink resolution failed for %s: %v", device, err)
+
+	var stat unix.Stat_t
+	if err := unix.Lstat(hostMapperPath, &stat); err != nil {
+		s.log.Errorf("cannot read stat of %s: %v", hostMapperPath, err)
+		return nil
+	}
+
+	switch stat.Mode & unix.S_IFMT {
+	// It is most common for devices under /dev/mapper to be symlinks, so check this first.
+	case unix.S_IFLNK:
+		linkTarget, err := os.Readlink(hostMapperPath)
+		if err != nil {
+			s.log.Errorf("symlink resolution failed for %s: %v", device, err)
+			return nil
+		}
+		return []string{"/dev/" + filepath.Base(linkTarget)}
+
+	// Devices under /dev/mapper can also be block devices.
+	case unix.S_IFBLK:
+		return s.findDMDeviceByMajorMinor(hostMapperPath, stat.Rdev)
+
+	default:
+		s.log.Errorf("unhandled file type for %s: %d", hostMapperPath, stat.Mode)
 		return nil
 	}
-	return []string{"/dev/" + filepath.Base(linkTarget)}
 }
 
 func (s *SysfsStorageInfoProvider) BuildBlockDeviceMetrics(timestamp time.Time) ([]BlockDeviceMetric, error) {

cmd/agent/daemon/pipeline/storage_info_provider_linux.go

@@ -0,0 +1,51 @@
+//go:build linux
+
+package pipeline
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/sys/unix"
+)
+
+// findDMDeviceByMajorMinor searches for the corresponding /dev/dm-* device
+// with the same major:minor numbers as the given device Rdev.
+func (s *SysfsStorageInfoProvider) findDMDeviceByMajorMinor(hostMapperPath string, rdev uint64) []string {
+	devDirPath := filepath.Join(s.hostRootPath, "/dev")
+	entries, err := os.ReadDir(devDirPath)
+	if err != nil {
+		s.log.Errorf("failed to read /dev directory: %v", err)
+		return nil
+	}
+
+	targetMajor := unix.Major(rdev)
+	targetMinor := unix.Minor(rdev)
+
+	for _, entry := range entries {
+		// We only care about device mapper devices.
+		if !strings.HasPrefix(entry.Name(), "dm-") {
+			continue
+		}
+
+		dmDevicePath := filepath.Join(devDirPath, entry.Name())
+		var dmStat unix.Stat_t
+		if err := unix.Stat(dmDevicePath, &dmStat); err != nil {
+			continue
+		}
+
+		// Check if it's a block device and has matching major:minor
+		if dmStat.Mode&unix.S_IFBLK != 0 {
+			dmMajor := unix.Major(dmStat.Rdev)
+			dmMinor := unix.Minor(dmStat.Rdev)
+			if dmMajor == targetMajor && dmMinor == targetMinor {
+				return []string{"/dev/" + entry.Name()}
+			}
+		}
+	}
+
+	s.log.Errorf("no matching /dev/dm-* device found for %s (major=%d, minor=%d)",
+		hostMapperPath, targetMajor, targetMinor)
+	return nil
+}

cmd/agent/daemon/pipeline/storage_info_provider_other.go

@@ -0,0 +1,7 @@
+//go:build !linux
+
+package pipeline
+
+func (s *SysfsStorageInfoProvider) findDMDeviceByMajorMinor(hostMapperPath string, rdev int32) []string {
+	return nil
+}